Scientists at Stanford University have improved the efficiency of a revolutionary solar cell by around 100 times. Unlike standard photovoltaic cells, which only capture light energy, Stanford’s new device captures both light and heat, potentially boosting solar cell efficiency towards 60% — way beyond the 30-40% limit of traditional silicon photovoltaic solar cells.

This new device uses a process called photon-enhanced thermionic emission (PETE). In photovoltaic cells, photons strike a semiconductor (usually silicon), creating electricity by knocking electrons loose from their parent atoms. The PETE process is similar, but also very different and altogether rather complex. In essence, think of it as the photovoltaic equivalent of a turbocharger.

A diagram of Stanford’s photon-enhanced thermionic emission (PETE) device. The yellow/gray sandwich at the top is the GaAs/AlGaAs cathode; the blue balls are photoexecited electrons; the gray slab is the anode; and the red/blue section represents a heat pipe, that leads to a steam turbine/Stirling engine.
To begin with, there’s a gallium arsenide/aluminium gallium arsenide (GaAs/AlGaAs) semiconductor sandwich at the top of the device. (The picture at the top of the story, incidentally, is a gallium arsenide wafer.) The top half of the sandwich is tuned to gather as much sunlight as possible, creating a lot of excited electrons using the photovoltaic effect. The underside is basically a sea of nanoantennae, which emits these photoexcited electrons across a vacuum to the anode. At the anode, the electrons are gathered and turned into an electrical current.